import heapq
n = int(raw_input())
p = map(float, raw_input().split())
q = map(float, raw_input().split())
q = [q[i] / 100. for i in xrange(n)]
ans = 0.0
que = [[-p[i] * q[i], i] for i in xrange(n)]
heapq.heapify(que)
i = 1
while i < 1000000:
    pq, j = heapq.heappop(que)
    ans += -i * pq
    p[j] *= (1.0 - q[j])
    heapq.heappush(que, [-p[j] * q[j], j])
    i += 1
print "%.10f" % (ans / 1000.)